1. Field of the Invention
The subject invention relates to cooling towers for air conditioning systems and industrial process cooling.
2. Description of the Prior Art
Air conditioning systems for large buildings employ cooling towers for carrying out a portion of the heat exchange that is essential to the cooling process. Industrial processes (e.g., chemical production, metals industry, plastics industry, food processing, etc.) generate heat that must be disposed of, often by use of cooling towers. The cooling tower is a housing that channelizes air in proximity to a heat exchange fluid. For example, a heat exchange fluid may be circulated through the cooling tower, and at least one fan may be mounted on the cooling tower to generate a flow of cooling air in proximity to the heat exchange fluid. Heat is transferred from the heat exchange fluid to the air, largely through the evaporation of a small percentage of fluid which substantially lowers the temperature of the primary heat exchange fluid. The cooled heat exchange fluid can then return to the process to perform a heat exchange function for either industrial process equipment or commercial air conditioning system.
The efficiency of an air conditioning system depends, in part, upon the heat exchange carried out in the cooling tower. Large buildings require large cooling towers, and in many instances an array of large cooling towers. Industrial processes depend on cooling towers to prolong the life of other equipment as well as produce top quality production.
The majority of prior art cooling towers are assembled from a plurality of pieces of sheet metal that are mounted to a metallic support frame. These prior art cooling towers typically are manufactured at a location remote from the installation site, and then are shipped to the installation site in a substantially assembled form. These large metallic prior art cooling towers are fairly heavy, and therefore require extensive structural support and greater transportation costs. Furthermore, the size and weight of prior art cooling towers complicates the hoisting and installation of the cooling tower onto the roof of the building. Costs of prior art cooling towers also are adversely affected by the labor intensive process for manufacturing and assembling the various metallic components of the prior cooling tower.
In addition to the cost penalties, the metallic sheet material used in prior art cooling towers generates significant vibration related noise due to the rotation of the fans and due to the flow of air through the cooling tower. Noise pollution often requires noise abatement measures that complicate the installation process and that further add to costs.
Prior art metallic cooling towers also are subject to corrosion or rust. Thus, prior art cooling towers have a relatively short life. Corrosion and rust problems can be avoided or deferred by employing corrosion or rust resistant alloys. However, these metallic materials further add significantly to the cost of the prior art cooling tower.
The prior art includes two types of cooling towers made with plastics. The first type of prior art plastic cooling tower is fabricated from a plurality of fiberglass reinforced polyester (FRP) panels that are fastened together. These plastic towers gain strength through the supplemental glass fiber in the plastic. FRP towers are generally more costly than the galvanized metal towers. Additionally these prior art towers have to be caulked at the seams, require many fasteners to hold the tower together and can develop leaks at the many joints.
The other type of prior art plastic towers are vertically oriented unitary cylinders. These towers can be very tall, with heights up to 19 feet. The ratio of the height to the cross-sectional area limits the cooling capability of the tower since cross-sectional are is more determinant of cooling capacity. The excessive height of these towers requires these prior art towers to be shipped with the axis of the cylinder oriented horizontally, which complicates off-loading and installation. These units have also been limited to one fan assembly per cylindrical unit.
In view of the above, it is an object of the subject invention to provide a cooling tower that is lighter weight and more durable than prior art cooling towers.
It is another object of the subject invention to provide a cooling tower that substantially avoids complex and costly assembly of components.
It is an additional object of the subject invention to provide a cooling tower that produces low levels of vibration related noise.
It is also an object to provide a unitary molded plastic tower that is not cylindrical and allows a much higher ratio of cross-sectional area to overall height.
It is also an object to provide a cooling tower that can be shipped fully assembled and upright to ease off-loading and installation.
Still a further object of the subject invention is to provide a substantially corrosion resistant cooling tower.
The subject invention is directed to a cooling tower that is made substantially from plastic. More particularly, a major portion of the cooling tower is defined by a tower shell that is unitarily molded from a suitable plastic, such as polyethylene. The unitarily molded tower shell may be formed by rotational molding. The tower shell may be molded to include air inlet louvers that are unitarily molded with the body of the tower shell. Additionally, short cylindrical flanges may be molded at the top of the tower shell for accommodating fans and necessary support housings for the fans. Apertures may be molded into the tower shell or may subsequently be cut into the tower shell for accommodating fluid pipes and/or conduits for electric cables. Separate fittings may then be mounted to these molded or cut apertures to accommodate connections with pipes or conduits. These separate fittings may be plastic or metal depending upon specifications of the heat exchange system.
The tower shell preferably is elongated and of polygonal cross-sectional shape, such as an octagonal cross-sectional shape. Thus, the cooling tower may include substantially parallel top and bottom surfaces that are aligned or alignable substantially horizontally. The tower shell may further include at least one vertically aligned or alignable side wall that is unitarily formed to extend continuously around the periphery of the tower shell. Angled connecting walls extend between the side walls and the respective top and bottom walls.
Tower shells in accordance with the subject invention may be of different respective lengths to accommodate different cooling demands. However, all of the tower shells may be of substantially constant longitudinal cross-sectional size and shape. Thus, a larger tower shell may differ from a smaller tower shell primarily by the length and by the number of cooling fans accommodated along the length. This use of a uniform cross-sectional shape for all tower shells enables the tower shells to be manufactured in the same or similar rotational molds. The molds may be rotatable about a horizontal axis and may be adapted to adjust the length of the mold by merely repositioning end wall portions of the mold.
The polygonal cross-section of tower shells in accordance with the subject invention enables a uniform width and depth for the fill material that performs the mass transfer function within the tower shell. Additionally, the tapered bottom portion of the polygonal tower shell defines a concave water sump at the bottom of the tower, while the tapered top section achieves an efficient exit air flow.
The tower also has several strengthening posts designed to provide structural stability where needed. These posts are a corrugated shape that provides more strength than a straight wall. Additional strength is created by conical ends that help support fan systems on the top of the tower.
Strength also is achieved by the rotational molding. In particular, the rotational molding of a structure as large as the subject cooling towers results in greater thicknesses at locations where surfaces meet at an angle. These greater thicknesses effectively define unitary fillets that add to the strength and vibration resistance. The fillets are particularly helpful at the peripheries of the top and bottom walls at the louvers, at the reinforcing flanges and where the fan-mounting flanges meet the top wall. Thus, the subject cooling towers avoid the complex assembling inefficiencies of the prior art and simultaneously enhance strength and efficiency at critical locations.
An alternate cooling tower employs the above-described rotational molding techniques, but is formed from two separately molded parts that can be assembled to one another. More particularly, the alternate cooling tower includes a base unitarily rotationally molded from a plastic material, such as polyethylene, and a main body unitarily rotationally molded from a plastic material, such as polyethylene. The base preferably includes a bottom wall, a side wall enclosure extending up from the bottom wall and an upwardly concave sump wall connecting upper ends of the side wall enclosure. The sump wall is spaced from the bottom wall in most locations to provide a double wall construction. However support ribs may extend between the bottom wall and the sump wall at selected locations. The base further includes a plurality of support posts projecting unitarily upwardly from the side wall. Each support post preferably is hollow and has a selected cross-sectional shape to achieve sufficient rigidity in the presence of loads applied thereto by the main body and the fans and to support external loads due to vibrations and wind. The posts are spaced from one another to define air inlets between the respective posts. Portions of each post remote from the side and bottom walls of the base or sump define outwardly and upwardly facing steps for supporting the main body.
The main body of the cooling tower in accordance with the second embodiment includes a top wall and a side wall enclosure extending downwardly from the top wall. The top wall preferably includes upper and lower panels and at least one fan support opening. The fan support opening preferably is characterized by a substantially cylindrical flange extending between the panels of the top wall. Fans can be mounted to the flange substantially as described with respect to the first embodiment. The side wall enclosure of the main body also may have inner and outer panels and a bottom edge remote from the top wall. The side wall enclosure is dimensioned to telescope over the top ends of the posts so that the bottom edge of the side wall enclosure can be supported on the steps at the top ends of the posts. Additionally, recesses may be molded between the inner and outer panels of the side walls adjacent the bottom edge for receiving portions of the posts that extend upwardly from the steps.
The side wall enclosure of the main body is further molded to include a plurality of reinforcing ribs or channels. The reinforcing ribs or channels are defined by a plurality of intersecting side wall panels that meet at selected angles. The rotational molding creates unitarily fillets similar to the fillets described with respect to the first embodiment. The fillets have a greater thickness of plastic material. Therefore the fillets provide reinforcement against vibration and enhanced structural rigidity. The reinforcing ribs or channels preferably are disposed to align with the support posts of the base.
The cooling tower of the second embodiment is assembled by positioning a fill material on the top of the posts. The fill material may be any conventional material used for cooling towers, and preferably is a high efficiency spiral wound PVC formed to include a plurality of corrugations that define complex flow channels. The main body then is telescoped onto the upper ends of the posts so that the bottom edge of the side wall enclosure of the main body is supported on the outwardly and upwardly facing steps defined on the respective posts. The portions of the posts spaced inwardly and upwardly from the steps slide into engagement with the recesses formed in the bottom edges of the side wall enclosure on the main body. Bolts or other fastening means can be directed through the side wall enclosure of the main body and into portions of the posts upwardly from the steps to securely fasten the main body to the base or sump portion of the cooling tower.
The double-panel construction and the recesses and support channels unitarily molded into the base and main body provide resistance against loads applied to the cooling tower, such as wind loads and vibration loads attributable to the rotation of the fans and the airflow created by the fans. The load resistance attributable to the recesses in the base and the channels in the main body is enhanced by the fillets created by the rotational molding process employed for both the base and the main body of the cooling tower. The cooling tower also provides a large inlet area between the posts for an inflow of air.